[bpf-next,3/5] bpf, lsm: Add function to read lsm hook return value range

Commit Message

Xu Kuohai March 16, 2024, 12:23 p.m. UTC

From: Xu Kuohai <[e-mail]>

Add function to read lsm hook return value range. The following patch
will use this information to check lsm hook return values in bpf
verifier.

Signed-off-by: Xu Kuohai <[e-mail]>
---
 include/linux/bpf_lsm.h |  8 ++++++
 kernel/bpf/bpf_lsm.c    | 56 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 63 insertions(+), 1 deletion(-)

Patch

diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index 1de7ece5d36d..e51c042abf43 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -9,6 +9,7 @@ 
 
 #include <linux/sched.h>
 #include <linux/bpf.h>
+#include <linux/bpf_verifier.h>
 #include <linux/lsm_hooks.h>
 
 #ifdef CONFIG_BPF_LSM
@@ -45,6 +46,8 @@  void bpf_inode_storage_free(struct inode *inode);
 
 void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func);
 
+int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
+			      struct bpf_retval_range *range);
 #else /* !CONFIG_BPF_LSM */
 
 static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
@@ -78,6 +81,11 @@  static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
 {
 }
 
+static inline int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
+					   struct bpf_retval_range *range)
+{
+	return -EOPNOTSUPP;
+}
 #endif /* CONFIG_BPF_LSM */
 
 #endif /* _LINUX_BPF_LSM_H */
diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index ee9d1a795334..7b4611fd3a37 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -11,7 +11,6 @@ 
 #include <linux/lsm_hooks.h>
 #include <linux/bpf_lsm.h>
 #include <linux/kallsyms.h>
-#include <linux/bpf_verifier.h>
 #include <net/bpf_sk_storage.h>
 #include <linux/bpf_local_storage.h>
 #include <linux/btf_ids.h>
@@ -40,6 +39,31 @@  noinline RET bpf_lsm_##NAME(__VA_ARGS__)	\
 #undef LSM_RET_INT
 #undef LSM_RET_VOID
 
+struct lsm_retval_desc {
+	unsigned long func_addr;
+	int minval;
+	int maxval;
+};
+
+#define LSM_RET_INT_ERRNO -MAX_ERRNO, 0
+#define LSM_RET_INT_ANY INT_MIN, INT_MAX
+#define LSM_RET_INT(defval, range_desc) LSM_RET_INT_##range_desc
+
+#define LSM_HOOK_RETVAL_int(NAME, ...) \
+{ (unsigned long)&bpf_lsm_##NAME, __VA_ARGS__ },
+
+#define LSM_HOOK_RETVAL_void(NAME, ...)
+
+#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
+LSM_HOOK_RETVAL_##RET(NAME, DEFAULT)
+
+static struct lsm_retval_desc lsm_retvalues[]  = {
+#include <linux/lsm_hook_defs.h>
+};
+#undef LSM_HOOK
+#undef LSM_RET_INT
+#undef LSM_RET_VOID
+
 #define LSM_HOOK(RET, DEFAULT, NAME, ...) BTF_ID(func, bpf_lsm_##NAME)
 BTF_SET_START(bpf_lsm_hooks)
 #include <linux/lsm_hook_defs.h>
@@ -399,3 +423,33 @@  const struct bpf_verifier_ops lsm_verifier_ops = {
 	.get_func_proto = bpf_lsm_func_proto,
 	.is_valid_access = btf_ctx_access,
 };
+
+static struct lsm_retval_desc *find_retval_desc(const char *func_name)
+{
+	unsigned long addr;
+	struct lsm_retval_desc *desc;
+
+	addr = kallsyms_lookup_name(func_name);
+	for (unsigned int i = 0U; i < ARRAY_SIZE(lsm_retvalues); i++) {
+		desc = &lsm_retvalues[i];
+		if (addr == desc->func_addr)
+			return desc;
+	}
+
+	return NULL;
+}
+
+int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
+			      struct bpf_retval_range *retval_range)
+{
+	struct lsm_retval_desc *desc;
+
+	desc = find_retval_desc(prog->aux->attach_func_name);
+	if (desc == NULL)
+		return -ENODEV;
+
+	retval_range->minval = desc->minval;
+	retval_range->maxval = desc->maxval;
+
+	return 0;
+}